1. Field of the Invention
The present invention relates in general to the field of making laminated components. More particularly, the present invention relates to a method of making laminated optical components having embedded optical elements. Specifically, a preferred embodiment of the present invention relates to a method of making the collimating backlight of a liquid crystal display system by replicating a plurality of optical elements in a layer of material and then laminating the replication side of the layer to a substrate with an index of refraction matching material, thereby embedding the optical elements within the collimating backlight. The present invention thus relates to a method of making optical components of the type that can be termed lamination embedding.
2. Discussion of the Related Art
Within this application several publications are referenced by arabic numerals within parentheses. Full citations for these, and other, publications may be found at the end of the specification immediately preceding the claims. The disclosures of all these publications in their entireties are hereby expressly incorporated by reference into the present application for the purposes of indicating the background of the present invention and illustrating the state of the art.
Historically, it was known in the prior art to replicate structural features in various polymeric materials..sup.(1) As is known to those skilled in the art, a master topography can be machined into a material, such as, for example aluminum or copper. Replicas can then be made from the master by pressing the master topography into a polymeric material. In the past, this replication process has been inefficient because the replicas were made individually. Thus, a previously recognized problem has been that large amounts of time are consumed in making a large number of replicas, resulting in a high per unit cost which did not decrease as the number of replicas made increased.
Needless to say, it is desirable to provide a method of mass producing replicas with higher efficiency. However, merely enhancing the efficiency of the replication step without considering any attendant increase in overall costs is not an adequate solution because the way in which the replication step is improved may involve more time, expense and/or energy than is saved due to improvements in the replication step.
For example, one unsatisfactory previous approach involves machining the master topography into an outer surface of a cylindrical unitary metal drum. The use of such a unitary metal drum might permit the replicas to be made continuously, thereby enhancing efficiency and quality. However, a disadvantage of this previously recognized approach is that such a metal drum is a single purpose tool. When there is no longer any demand for a particular replica, the metal drum cannot be adapted for another use because the master topography is an integral part of the drum itself.
Moreover, this previously recognized solution also has the significant disadvantage of high initial cost. The cost of machining the metal drum can easily be more than the savings incurred from the use of a continuous replication step, especially where a moderate number of replicas will be made, or where the replication features to be machined into the surface of the drum are numerous and/or very small. From a business point of view, the decision of whether or not to invest in such a unitary metal drum can be problematic where the individual orders in-hand for a particular type of replica do not justify the cost of machining a unitary metal drum. Therefore, what is needed is a method that replicates a surface topography with enhanced overall cost effectiveness, where the number of replicas to be made is, at best, uncertain.
The manufacture and sale of replicas is a competitive business. A preferred solution will be seen by the end-user as being cost effective. A solution is cost effective when it is seen by the end-user as compelling when compared with other potential uses that the end-user could make of limited resources.
Liquid crystal displays of the type hereunder consideration, sometimes called LCDs, are well-known to those skilled in the art..sup.(2,3) An LCD can be illuminated from the back so that the LCD can be viewed under conditions of low ambient lighting. For example, a backlight that includes one or more fluorescent light bulbs can be located behind the LCD.
A previously recognized problem has been that the light from the backlight must be polarized in order for the LCD to function properly. One approach, in an attempt to solve this polarization problem, involves providing a polarizing sheet between the backlight and the LCD. However, a major disadvantage of this approach is that a large amount of the available light from the backlight is not transmitted through the polarizing sheet, thereby resulting in decreased brightness.
To address the decreased brightness disadvantage discussed above, one approach has been to provide a plurality of optical elements in the bottom surface of the backlight. The purpose of these optical elements is to condition the light from the backlight before it reaches the polarizing sheet. By providing these optical elements, less power is lost when the collimated light passes through the polarizing sheet and the brightness of the LCD is enhanced.
However, this approach has the significant disadvantage of relatively high cost. Specifically, the cost of providing the optical elements on the bottom surface of the backlight is too high. For example, injection molding such a backlight requires expensive tooling and several minutes of production time for each molding. Further, the cost of tooling is even higher where a large number of optical elements are to be formed on each backlight or where the size of each of the optical elements is small. Therefore, what is also needed is a method of mass producing optical elements in an LCD backlight with enhanced overall cost effectiveness. Heretofore the abovediscussed requirements have not been fully met.
The below-referenced U.S. patents disclose embodiments that were at least inpart satisfactory for the purposes for which they were intended. The disclosures of all the below-referenced prior United States patents in their entireties are hereby expressly incorporated by reference into the present application for purposes including, but not limited to, indicating the background of the present invention and illustrating the state of the art.
U.S. Pat. No. 5,396,350 discloses a backlighting apparatus employing an array of microprisms. U.S. Pat. No. 5,390,276 discloses a backlighting assembly utilizing microprisms. U.S. Pat. No. 5,371,618 discloses a color liquid crystal display employing dual cells. U.S. Pat. No. 5,359,691 discloses a backlighting system with a multi-reflection light injection system. U.S. Pat. No. 5,056,892 discloses a totally internally reflecting thin flexible film.